JPH0113975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device that provides a movement in which one of a tool electrode and a workpiece is pushed in the direction of being pushed relative to the other, and a device that provides a motion in a direction perpendicular to the direction in which the tool electrode and the workpiece are pushed. The present invention relates to an improvement of an electrical discharge machining machine equipped with the following.

Conventionally, in electric discharge machining machines, relative movement is applied to the electrode and the workpiece in the direction in which the electrode is pushed into the workpiece, and the distance between the electrode and the workpiece is usually kept constant in that direction. Machining is performed while using the servo. Here, in normal electric discharge machining, after rough machining, finishing machining is performed using a plurality of similar electrodes with slightly different dimensions.
This is because in rough machining, the machining speed is high but the machined surface is rough, while in finishing machining the machined surface is fine but the machining speed is low, and the side gap between the electrode and the workpiece is narrower in finishing machining. This is due to Therefore, the following devices have been proposed for the purpose of processing from rough machining to finishing machining using a single electrode. In other words, after rough machining is completed, the electrode or the workpiece is given a movement with an element perpendicular to the normal feed direction, for example, an orbital circular motion, in the same way as using an electrode with a large apparent size. The same electrode used for rough machining is also used for finishing machining. This is, for example, as shown in FIG. 1, in which an electrode 10 and a workpiece 12 are placed opposite each other in an insulating liquid, and a pulsed current is supplied from a pulsed current supply device 14 to the machining gap. Process 12. At that time, the electrode 10 is connected to the voltage differential circuit 1
6. A servo circuit consisting of an amplifier 18 and a hydraulic servo valve 2 driven by the output signal of the circuit.
0, the direction in which the workpiece 12 is pushed into the workpiece 12 (Z
In the axial direction), for example, the machining progresses by feeding so that the voltage Vd in the machining gap matches the reference voltage Vs on average.

Note that the reference voltage Vs is set to a value suitable for the width of the machining gap to be appropriate and for normal discharge to occur.

After the rough machining is completed to a depth set slightly before the final desired depth, the energy of one pulse of the pulse current supply device 14 is changed to be smaller, and the electrode motion control device 24 is further controlled by a known method. The servo motors 26, 28 are operated, thereby causing the X-Y cross tables 30, 32 to perform continuous circular motion. In this case, it is sufficient to apply a sine wave to the servo motors 26 and 28 having a voltage having a phase difference of π/2 and an amplitude corresponding to the difference in side gap between rough machining and finishing machining. Then, while the electrode 10 and the workpiece 12 are relatively orbiting in a circular motion in this manner, processing is performed again to a desired depth. In this case, the effect is equivalent to expanding the diameter of the electrode 10 by a dimension corresponding to the diameter of the relative orbital circular motion, so the rough machined surface caused by the previous rough machining is removed. be. here,
When using this method to machine a corresponding hole on a workpiece 12 using an electrode 10 having an elliptical cross section as shown in FIG. The amount of 12 to be removed is much greater in the areas where the electrode 10 has a large radius of curvature than in the areas where it has a small radius of curvature. Therefore, as the machining progresses, the machined depth of the portion with a large radius of curvature and the machined depth of the portion with a small radius of curvature become significantly different, as shown in FIG.

In other words, if the elliptical electrode 10 is used to perform a revolution circular motion with the radius of the circular motion corresponding to a predetermined machining allowance from the beginning, the removal rate of the workpiece due to electric discharge is constant, so the Therefore, there will be a difference in the amount of processing. In other words, when the orbital circular motion is constant, the area to be machined is large in parts with a large radius of curvature, and the area to be machined in parts with a small radius of curvature is smaller than that of large parts, so the machining speed ( Assuming that the removal rate (removal rate) is constant, machining progresses quickly in small areas to be machined, and slowly in large areas. In other words, the depth of machining is small in areas where the area to be machined is large, and the depth of machining is large in areas where the area is small. FIG. 3 is a perspective view of the locus of the orbital motion between the electrode and the workpiece at different depths. When the depth is zero, circular motion is performed within the XY plane, but as machining progresses, a locus is generated that is a combination of the circular motion and the difference in machining depth on the Z axis.

Therefore, when machining deep holes with such equipment, it is not possible to sufficiently remove the rough machined surface from the previous rough machining, and the depth reached by the electrode during finishing machining is It has a major drawback in that there are differences in each part depending on the shape.

In addition, in this conventional example, processing in which the radius of the revolution of the tool electrode gradually increases, but when the tool electrode processes the outer periphery of the workpiece,
That is, a similar drawback occurs when the radius of revolution of the tool electrode gradually decreases.

Therefore, in order to solve this drawback, an apparatus that employs the following processing method has been proposed.
FIG. 4 is a diagram explaining this processing method. Second
In machining by orbital motion using the electrode structure shown in the figure, it is clear that the cause of the defect explained using Figure 3 is the difference in machining allowance on the X-Y plane as seen from the Z-axis. The processing method using the explanatory diagram shown in FIG. 4 solves this problem.

That is, the spiral circle shown in FIG. 4 is a diagram showing the relative movement locus of the orbital circular motion between the electrode 10 and the workpiece 12, and the amount of increase in machining allowance per revolution is shown as ΔR. First, processing is performed until the electrode reaches its deepest position in the Z-axis direction. After that, machining will be performed using orbital circular motion, and the machining allowance increase ΔR
Gradually increases the amount of revolution until the desired amount of revolution is reached.

Here, if ΔR is made extremely small, the machining allowance per hit will be extremely small, and machining energy will be spared, resulting in uniform machining. If this is done, the situation shown in FIG. 3 will not occur. However, having a margin means that the machining proceeds below the machining capacity, and as a matter of course, the machining time takes longer and the machining efficiency decreases.
If ΔR is increased to prevent this, the machining allowance will increase, and if the machining allowance exceeds the machining capacity,
After all, the situation shown in FIG. 3 described above occurs, which is a problem.

The present invention was made in view of the above-mentioned conventional problems, and its purpose is to process the increase in machining allowance ΔR for each revolution when one of the tool electrode and the workpiece is moved in a revolving manner relative to the other. It is an object of the present invention to provide an electric discharge machining machine that performs good finishing machining and has sufficient machining efficiency by optimally controlling it according to its capacity.

To achieve the above object, the present invention revolves one of the tool electrode and the workpiece relative to the other, and gradually expands or contracts the movement path by a predetermined amount until a desired amount of revolution is reached. In a processing machine that performs machining, the tool electrode is in a machining state where the machining gap is appropriate with respect to the workpiece and discharge normally occurs during the revolution movement, or the machining gap is wide and no discharge occurs. A discriminating device for discriminating whether machining is not possible based on a detected voltage between the tool electrode and the workpiece; and at least two types of predetermined amounts for enlarging or contracting the movement path, and the discriminating device is capable of machining. a motion path determination device that expands or reduces the motion path based on the smaller set value when the state is determined, and expands or contracts the motion path based on the larger set value when the state is determined to be unprocessable; It is characterized by having the following.

Next, preferred embodiments of the present invention will be described based on the drawings. Note that the same reference numerals are given to the parts corresponding to those of the conventional device described above, and the explanation thereof will be omitted.

FIG. 5 shows an embodiment of the electrical discharge machining machine of the present invention.

Here, the X-Y cross tables 30 and 32 are operated by driving the servo motors 26 and 28 in response to a signal from the electrode motion control device 24, and a relative position is created between the electrode 10 and the workpiece 12. Providing the orbital circular motion is similar to the conventional device shown in FIG. 34 is a differential transformer.
This differential transformer 34 is configured such that its coil portion is fixed to the fixed side of the machine, and its movable iron core moves in the same manner as the electrode 10, and the height of the electrode 10, that is, the position in the Z-axis direction, is detected. be done. Further, 36 is a circuit similar to that shown in FIG. 12 of Japanese Patent Publication No. 53-32112, for example, in which the difference voltage Vd-Vs between the machining gap voltage Vd and the reference voltage Vs and the output of the differential transformer 34 are connected. This is a comparison selection circuit for preferentially selecting the lower one among them. Here, the operation of the comparison selection circuit 36 is as detailed in this Japanese Patent Publication No. 53-32112, by setting in advance the position of the coil portion of the differential transformer 34 fixed on the fixed side of the machine. If the electrode 10 is above the set position, the voltage Vd at the machining gap and the reference voltage
The position of the electrode 10 is controlled according to the differential voltage Vd-Vs with respect to Vs, and when the electrode 10 descends to the set position, the output of the differential transformer 34 is selected preferentially, and the
The electrode 10 is controlled so as not to fall below that position by a servo mechanism consisting of the following.

FIG. 6 is an explanatory diagram of the control device 24 of the X-Y cross tables 30, 32. Here, 4
0 is a two-phase oscillator, which generates sine waves with a 90° phase difference.
Outputs e _x and e _y . 42 is the electrode voltage detection signal
This is a control circuit for controlling outputs e _x and e _y based on Vd and extracting voltages e _x and e _y corresponding to a desired eccentric radius. The voltages of E _x and E _y are added at the addition point 44,
The summation point outputs are amplified by motor drive amplifiers 47 and 48 to drive the X and Y axis motors 26 and 28, respectively. Linear potentiometers R _x and _Ry are mounted on the X-Y cross tables 30 and 32 and are used to detect the position of the electrode 10 on the X-Y plane. linear potentiometer
The output voltages of R _x and R _y are the summation points 44 and 46 mentioned above.
Since the feedback is given to
The motors 26 and 28 move until the output voltage becomes 0, and the table position is determined by the output E _x , E _y of the control circuit 42
is controlled to be equal to .

FIG. 7 is a detailed explanatory diagram of the two-phase oscillator 40. This two-phase oscillator 40 includes an integrating circuit consisting of an operational amplifier Q ₁ , a resistor R, and a capacitor C, and a limiting inversion circuit consisting of an operational amplifier Q ₂ , a resistor R, a capacitor C, and voltage-limiting Zener diodes ZD ₁ and ZD ₂ . and an integrator are cascaded in a feedback loop that provides the following differential equation:

RCd/dte _X = e _Y ... _{( 1} ) RCd/dte _Y = _-e It's stable. Also, Zener diode for voltage limiting
ZD ₁ and ZD ₂ prevent the waveforms of e _X and e _Y from being distorted and stabilize the amplitude. The two outputs e _X and e _Y thus obtained have a phase difference of 90° and are expressed by the following equation.

e _X = E sin t/RC (3) e _Y = E cos t/RC (4) Here, E is the voltage of the voltage limiting Zener diodes ZD ₁ and ZD ₂ . Furthermore, in order to set the frequency, external terminals are provided at both ends of the resistor R in this circuit, and external resistors 50 and 52 are connected to these external terminals. And this external resistance 50,5
By setting the resistance value of 2, frequency control can be performed externally.

FIG. 8 is a detailed explanatory diagram of the control circuit 42.
Generally, while electrical discharge machining is being smoothly performed between the electrode 10 and the workpiece 12, the inter-electrode voltage detection signal Vd is within a certain range. Then, as the discharge gap becomes wider, the detection signal Vd becomes larger, and when the discharge gap exceeds a certain level, it becomes impossible to perform a good discharge. The voltage at which the detection signal can be processed at this time
Defined as V ₁ . Furthermore, if a short circuit occurs during electrical discharge machining, the detection signal Vd decreases to below a certain value. The detection signal at this time is defined as short circuit detection voltage _V2 .

In addition, processable voltage V ₁ and short circuit detection voltage V ₂ are as follows:
It may be set as an average voltage of several mSEC corresponding to the inter-electrode voltage detection signal Vd. By setting the machinable voltage V ₁ and the short-circuit detection voltage V ₂ in advance and comparing these with the detection signal Vd, it is possible to determine whether or not electric discharge machining is being performed properly.

First, the detection signal Vd is compared with the machinable voltage V ₁ in the comparator 60, and if it is larger than the voltage V ₁ , the gap between the electrode 10 and the workpiece 12 has widened to the extent that no electric discharge occurs, and the machining is impossible. It is determined that Then, the comparator 60 outputs a logic level "0", and the gate of the AND gate 62 is closed and connected through the inverter 64.
AND gate 66 is opened. AND gate 62,
66 is applied with a clock pulse CP from an oscillator 68 at regular intervals or a clock pulse CP synchronized with the oscillation cycle of the output of the two-phase oscillator 40, and when processing is not possible, a clock pulse CP is applied to the first counter 70.
This clock pulse is input via OR gate 72 and counted. Further, when the detection signal Vd is lower than the machinable voltage _V1 , the gap is a distance that allows sufficient discharge, and it is determined that the machining state is possible.
At this time, the comparator 60 is at logic level "1"
is output, the AND gate 62 opens, and the second counter 74 starts counting. These counters 70 and 74 are connected in cascade, and the output counted by the counter 74 is further counted by the counter 70. Further, the detection signal Vd is compared with the short circuit detection voltage V ₂ in the comparator 76.
When the detection signal Vd falls below the short circuit detection voltage _V2 , it is determined that a short circuit phenomenon has occurred, and the comparator 76 outputs a logic level "0" and closes the AND gates 62 and 66, so that the counters 70 and 74
The value of does not increase. In this way, a determination device is configured that determines whether or not the electrode 10 is in a state where it can process the workpiece 12.

The outputs of counters 70 and 74 are multiplication type
It is input to the DA converters 78X, _78Y , and the values of the output _e
Multiplication by a count value of 4 is performed, and the analog quantities of the multiplication values are output as _EX and _EY . As such a multiplication type DA converter, AD7520 manufactured by Analog Devices, Inc. of the United States is known. With the above configuration, multiplicative DA
The peak values of _the outputs _E
It increases slightly by 1 unit in response to the input of CP, and increases by 4 units in response to the input of clock pulse CP in a state where machining is impossible due to a wide machining gap.
Additionally, if a short circuit condition is detected, the output _EX ,
The peak value of E _Y does not increase. In this way, the multiplication type DA converters 78X and 78Y function together with the counters 70 and 74 as a motion path determining device.

This embodiment has the above-mentioned configuration, and its operation will be explained below by taking as an example a case where a hole is machined in a workpiece 12 using the electrode 10.

First, in the rough machining process, the energy per pulse of the pulse current supply device 14 is greatly controlled, and machining is performed until a desired machining depth is reached in the Z-axis direction.

Simultaneously with the completion of this rough machining step, the energy per pulse of the pulse current supply device 14 is controlled to a small value, and the electrode motion control device 24 controls the X-
A finishing process is started in which the Y cross tables 30 and 32 are given continuous orbital circular motion. Here, the radius of the orbital circular motion given to the X-Y cross tables 30, 32 is controlled so as to gradually increase by ΔR from 0 as shown in FIG.
Then, this increase amount ΔR is controlled so that it is within the range of the processing capacity of the apparatus and the processing efficiency is maximized.

First, the two-phase oscillator 40 outputs sine waves e _X and e _Y having phases different by 90 degrees. These outputs e _X and e _Y are the multiplier DA converters 78
is multiplied by the outputs of counters 70 and 74,
The driving voltages _EX and _EY of the servo motors 26 and 28 are output. Then, based on the voltage peak values of the outputs EX _and E _Y , the X-Y crosstables 30 and 32
, that is, the radius of the orbital circular motion of the electrode 10 with respect to the workpiece 12 is given.

Here, the radius of the orbital circular motion gradually increases as follows. First, at the start of finishing processing, the outputs of the counters 70 and 74 are 0, so the outputs of the multiplication type DA converters 78X and 78Y
_EX and _EY are also 0. Therefore, the orbital circular motion starts from a point where the radius is zero. When the machining voltage detection signal Vd is in the range of V ₁ >Vd <V ₂ , the comparators 60 and 76 determine that the machining state is such that electrical discharge machining is being performed satisfactorily. Then, the comparators 60 and 76 both output logic level "1", the AND gate 62 is opened, and the counter 7 is output through the AND gate 62.
0,74 starts counting clock pulses CP. Then, the multiplication type DA converter 78X, 7
8Y increases the peak values of EX _{and EY} by 1 unit in response to the clock pulses CP input to the counters 70 and 74, and the radius of the orbital circular motion also increases gradually by ΔR ₁ .

Further, when the machining voltage detection signal Vd is in the range of Vd>V ₁ , the comparator 60 determines that the machining gap is too wide and the discharge is not performed satisfactorily, making machining impossible. Then, comparator 60 outputs a logic bell "0", closes AND gate 62, opens AND gate 66, and causes counter 70 to directly count clock pulses CP. Then, as is clear from the drawing, the counters 70 and 74 count one clock pulse CP at a rate four times higher than when they are in the machining ready state. Therefore, the multiplication type DA converters 78X and _78Y convert _E
The radius of the orbital circular motion of the electrode 10 gradually increases by an increase amount ΔR ₂ (ΔR ₂ =4ΔR ₁ ), which is four times that when the electrode 10 is in the machinable state.
As a result, the machining gap between the electrode 10 and the workpiece 12 is rapidly narrowed to a range where electrical discharge machining is possible. Then, when entering the machining enabled state, the machining voltage detection signal Vd becomes V ₁ >Vd, and the operation switches to the machining enabled state described above.

Further, if a short circuit occurs between the electrode 10 and the workpiece 12 due to the machining gap being too narrow, for example, the machining voltage detection signal Vd becomes V ₂ >Vd, which is detected by the comparator 76 and
6 outputs logic level "0". Then,
AND gates 62, 66 are closed and counter 70,
Counting of 74 clock pulses CP is stopped. As a result, the multiplication type DA converter 78X,
The increase in the peak values of the outputs EX and E _Y of 78Y is temporarily stopped, and the radius of _the orbital circular motion of the electrode 10 also does not increase. When this short circuit is removed by continuing the orbital circular motion of the electrode, the machining voltage detection signal
Vd returns to Vd< _V2 , and the operation switches to the machining state described above.

In this way, finishing processing is performed while the processing gap between the electrode 10 and the workpiece 12 is always maintained at an appropriate value.

In this embodiment, a process in which the radius of the revolution of the tool electrode gradually expands has been described, but the present invention is not limited to this, and can also be used in cases where the tool electrode processes the outer periphery of a workpiece. In this case, the radius of the revolution of the tool electrode will gradually decrease, but it is sufficient if the counter used is of a subtraction type instead of an addition type.

In addition, in this example, the workpiece was fixed and the tool electrode was moved in revolution, but
Conversely, the same effect can be obtained by fixing the tool electrode and causing the workpiece to revolve.

As described above, according to the present invention, when one of the tool electrode and the workpiece is caused to revolve around the other, it is determined whether or not the tool electrode is in a machinable state with respect to the workpiece, By optimally controlling the amount of increase in machining allowance for each round according to the state, it is possible to perform good machining and to obtain an electrical discharge machining machine with good machining efficiency.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional electric discharge machining device, Fig. 2 is an explanatory diagram showing an example of its electrode structure, Fig. 3 is a machining explanatory diagram showing a problem when using the electrode shown in Fig. 2, Fig. 4 is an explanatory diagram showing the trajectory when the electrode is given a revolving circular motion whose radius automatically expands, Fig. 5 is an explanatory diagram of an electric discharge machining device showing an embodiment of the processing machine of the present invention, and Fig. 6 The figure is an explanatory diagram of the control device for the X-Y crosstable, FIG. 7 is a circuit diagram of the two-phase oscillator, and FIG. 8 is a circuit diagram of the control circuit. The same members in each figure are given the same symbols, 10 is a tool electrode, 12 is a workpiece, 60 is a comparator,
62 is an AND gate, 64 is an inverter, 66 is an AND gate
70 is a first counter, 74 is a second counter, and 78X and 78Y are multiplication type AD converters.

Claims (1)

[Claims] 1. Move the tool electrode in the direction in which it is pushed into the workpiece, and also make it revolve in a direction perpendicular to that direction, and gradually expand or contract this orbital movement path by a predetermined amount to achieve the desired amount of revolution. In an electric discharge machine that performs machining until reaching , the tool electrode is in a machining state where the machining gap is appropriate and discharge occurs normally with respect to the workpiece during the revolution movement, or the machining gap is wide and discharge is possible. a discriminating device for discriminating whether machining is not possible in a state in which no When the discrimination device determines that machining is possible, it expands or reduces the orbital motion path based on the smaller set value, and when it determines that machining is impossible, it expands or reduces the orbital motion path based on the larger set value. An electric discharge machining machine characterized by comprising: a movement path determining device for reducing.